From this solution the quinine is separated by adding carefully, by means of a pipette, the above-mentioned solution of the iodosulphate of chiniodine, as long as a dark brown-red precipitate of iodosulphate of quinine-herapathite
is formed. As soon as all the quinine has been precipitated, and a slight excess of the reagent has been added, the liquor acquires an intense yellow colour. The beaker containing the liquor with the precipitate is now covered by a watch-glass, and heated on a water bath till the liquid begins to boil.
After cooling, the beaker is weighed, to ascertain the amount of liquid which is necessary in order to be able to apply later the above-mentioned correction. For although quinine-herapathite is very little soluble in alcohol, it is not insoluble, and therefore a correction must be applied for the quantity which has been dissolved both by the alcohol used for the solution of the alkaloids and the alcohol contained in the reagents.
The liquor is now filtered to collect the iodosulphate of quinine on a small filter, where it is washed with a saturated solution of herapathite in alcohol. After the washing has been completed, the weight of the funnel with the moist filter is taken, and the filter allowed to dry in the funnel. As soon as it is dry the weight is taken again, to ascertain the amount of solution of herapathite which remained in the filter, and which left the dissolved herapathite on the filter after the evaporation of the alcohol.
This amount is subtracted from the total amount of liquid, and for the remaining the correction is calculated with reference to the temperature of the laboratory during the time of the analysis. The dry iodosulphate of quinine is taken from the filter and dried on a water bath, in one of a couple of large watch-glasses closing tightly upon each other, so that the weight of the substance contained in the glass may be taken without the access of air.
When, after repeatedly ascertaining the weight, it remains constant, this weight is noted down, and to it is added the product of the calculated correction. The sum of this addition is the total amount of iodosulphate of quinine obtained from the mixed alkaloids subjected to the operation, and from this weight the amount of crystallisable quinine can be calculated by the use of Hauer’s formula, 2C40H24N2O43(HO1SO3), 31 (old notation), which the author has found to be correct. According to this formula, 1 part of iodosulphate of quinine, dried at 100° C., represents 0·5509 per cent. of anhydrous quinine, or 0·7345 per cent. of disulphate of quinine.
The accuracy of this determination may be seen from the following examples:
0·24 gram of anhydrous crystallised quinine gave 0·541 gram of herapathite dried at 100° C. = 0·298 gram of quinine.
According to Hauer’s formula, 0·5336 gram of herapathite = 0·294 gram of quinine, which ought to have been obtained.
1·048 gram of bitartrate of quinine gave